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honestly, maybe this reflects my americanness but I presumed it was derived from the (western film/culture) word, a corruption of 'get'. Today I learned that it means something else in british.

You can hardly watch more than a few hours of british comedy without someone being called a 'stupid git' at some point.

Sadly my consumption of British comedy has been -it crowd (of course), -monty python, and -mr bean (no words)

It's such a short word I'd probably have missed it or misheard it as 'cad' or something.

Or listen to the Beatles https://genius.com/836309

Oh huh, I didn't realize it didn't mean the same in American English. I guess I knew it, I just never realized it.

I learned about the British meaning from reading the Harry Potter books.